Optical fabrication and Optical manipulation
of semiconductor nanoparticles
Ashida lab. Nawaki Yohei
2
Contents• Introduction
– Optical fabrication and manipulation– Advantage of particles– Photo Induced force– Resonant force
• Purpose– Previous study– My study
• Experimental setup– Ablation and Manipulation– Scanning electric microscopy
• Optical fabrication– Tablet of GaN– Crystal of GaN
• Optical manipulation– Zinc oxide
• Summary
3
Ablation and manipulationIntroduction
Ablation laser
Manipulation laser
AblationFabrication method of particlesusing laser sputtering
ManipulationTransporting method by the resonant radiation force
Si substrate
Low-dimensional structures4Introduction
DO S DO S DO S DO S
E E E E
Bulk Thin film Quantum wire Nano particle
enhancement of oscillator strength
Photo induced force5Introduction
Gradient Force
Scattering and Absorption pressure
Optical axis
Photo induced forceGradient forceScattering and Absorption pressure
Photo induced force: 光誘起力Gradient force: 勾配力Scat. And abs. pressure: 散逸力
Gradient force6Introduction
The force pushing objects to the focal point
Stabilization point
Electrical gradient
Gaussian beam
Scattering and Absorption force7Introduction
The force arising from the momentum transfer from the light
ℏ𝜈 power
scattering
absorption
Manipulation in various scale8Introduction
MicroparticleNanoparticleAtom
1mm~1nm~1mm~1nm
Optical tweezers
Structural dependenceNo Structural dependence
Laser cooling
No resonanceresonance
Structural dependence
resonanceor
No resonance
It’s difficult for optical
manipulation.
Energy of applied light≠
Energy of exciton level
Energy of applied light=
Energy of exciton level
Resonant or Non-resonant light9Introduction
Non resonant ResonantResonant Resonant
𝐸=𝐸𝑔−𝐸𝑏+∆𝐸
∆𝐸=𝜋 2ℏ2
2𝑀𝑎2
E
a
Enhancement by resonant light10Introduction
Ref: T.Iida and H. Ishihara Phys. Rev. Lett. 90, 057403 (2003)Using resonant lightPhoto induced force is drastically enhanced.
Numerical calculation example (CuCl)
100 times of gravitational acceleration
Previous study11Purpose
Our group has succeeded manipulation of nanoparticles
Wide-gap semiconductorCuCl ZnO
K. Inaba phys.stat.sol. (b)243, No.14, (2006) S. Okamoto master thesis (2011)
My study12Purpose
GaN bulk
GaN particles
Manipulated GaN particles
ablation
manipulation
Fabrication method13Experimental setup
Nd:YAG
Ti:sapphire
ablation laser
manipulation laser
wavelength :525nmpulse duration :10ns
SHG
wavelength :726nm
cryostat
Si substrate
sample
back substrate
front substrate
Vacuum state (300K)
Superfluid He state (2K)wavelength :718nm
pulse duration :100fs
Observation method14Experimental setup
Electron beam
Secondary electron
sample
Character X-ray
Cathode Luminescence
SEM measurement
CL measurement
Energy Dispersive X-ray Spectrometry
Scanning electron microscope
Scanning electron microscope: 走査型電子顕微鏡Secondary electron: 二次電子Cathode luminescence :電子線励起による発光Character X-ray: 特性 X線
To analyze element
To take 2D image
Optical fabrication
15
Gallium Nitride16Ablation
GaN: 3.4eV cf. ZnSe, SiC, ZnO, CuClGaN has wide controllable range of bandgap
with ternary crystal semiconductor InN, AlN.0.7eV~6.1eVCrystal growth is difficult
Blue- and UV-Light emitting diode and laser
Wide-gap semiconductor
Tablet of GaN17Ablation
Press!
Powder Tablet
SEM images18Ablation
Ablation conditionsVacuum stateNd:YAG power 0.5mJ
I could fabricate particles...
Element analysis19Ablation
EDS data
Ga mapping image
SEM image
Nitrogen peak was expected.
20
Particles were oxidized.
Crystal of GaN21Ablation
Crystal
Tablets included many impurity.
The reason why is that oxidized particle were fabricated.
The surface of powders were oxidized.
I used crystal of GaN
SEM image22Ablation
Vacuum stateAblation conditions
Nd:YAG power :1.5mJ
Element analysis23Ablation
A broken piece by ablation
Ga mapping image
SEM image
EDS data
Nitrogen was observed.
Element analysis24Ablation
Fabricated particle by ablation
Ga mapping image
SEM image
EDS data
Nitrogen peak was expected.
25
Particles have nitrogen defect.
Superfluid Helium condition26Ablation
Superfluid HeliumLow temperature
Viscosity becomes zero.
Resonant energy very sharp
Small destabilizing effect
Suitable for optical manipulation The particles can be cool rapidly.
For ablation
Crystal of GaN27Ablation
Superfluid He stateAblation conditions
Nd:YAG power 0.5mJ
Crystal of GaN28Ablation
Ga mapping image
SEM image
Nitrogen peak was expected.
EDS data
29
Particles have nitrogen defect.
Results30Ablation
The particles had nitrogen defect and contained oxygen.
Tablet from powderVacuum conditionsuperfluid He condition
In such condition
CrystalVacuum conditionsuperfluid He condition
Optical manipulation
31
Zinc Oxides32manipulation
Band-gap energy of ZnO is 3.4eV.
Wide-gap semiconductor
1mm
1 cm
Polygonal shape
ZnO is very stable material, because It’s oxidation products.
Problem of size distribution33manipulation
Advantage of particle Density of state
Size distribution
Density of state becomes cloudy.
Density state become sharply.
Pulse laser spectra34manipulation
3.35 3.36 3.37 3.38 3.39 3.40
Inte
nsity
(a.u
.)
Photon energy(eV)3.35 3.36 3.37 3.38 3.39 3.40
Inte
nsity
(a.u
.)
Photon energy (eV)
Pulse durationPeak energySpectrum width
1ps100fs3.38eV3.38eV
2meV20meV
fs pulse laser ps pulse laser
Resonance radiusunder 100nm radius specific radius
Y. Saito Master thesis (2009)
Decrease of size distribution35manipulation
Y. Saito Master thesis (2009)
0 10 20 30 40 50 60 70 80 90 1000
2
4
6
8
粒子数
(nm)粒子直径
0 10 20 30 40 50 60 70 80 90 1000
2
4
6
8
10
12
粒子数
(nm)粒子直径
fs pulse laser ps pulse laser
The Size distribution reduced in response to spectrum width.
I try to measure size distribution from spectrum width of
photoluminescence.
Summary36
Optical fabricationI can’t fabricate GaN particles
Optical manipulation
The particles fabricated by ablation have nitrogen defect and contained oxygen.
I try to measure size distribution from spectrum width of photoluminescence.
Appendix
37
38
Photo induced forceAppendix
bscat nmmr
cIF
2
2
2
4
650
21
3128
Gradient force
Radiation pressure
22
2332
21
22E
mmrnEnF bb
grad
Optical letters vol.11, No. 5, 288 (1986)
First experiment39Appendix
transparent latex spheressize
material
0.59, 1.31, 2.68mm
CW argon laser = 0.5145mmw0= 6.2mmPower 19mW
The author measured sphere moved at 26±5mm/sec
samples
laserTEM00
Laser cooling40
Quantum confinement41Appendix
a > ab
a :ドット半径ab :励起子ボーア半径
∆𝐸=ℏ2𝜋 2
2𝑀𝑒𝑥𝑎2
ドット内に励起子が閉じ込められる
2a 2ab
ΔE量子サイズ効果によりエネルギーレベルが変化
2a
弱閉じ込めモデル
2a2ab
ab > a強閉じ込めモデル
励起子ボーア半径CuClドット半径
0.68nm数 nm
弱閉じ込めモデル
励起子の重心運動が量子化